I interchange the 2 batteries that you mentioned between the MKIV and the 1DX and I haven't had a problem.
As Neuro has pointed out the LP-E4N will charge to about 90%. The MKIV doesn't drain the batteries as quickly as the 1DX, so you should be just fine with the 90% charge and if you do eventually purchase a 1DX then the new LC-E4N charger will come with it. $438 Euros is a lot of money for the charger, so if you need the 100% charge (depending on your needs), it's cheaper to exchange for the older LP-E4 battery and save some money instead of buying the new charger.
P.S. I have both chargers since they came with the cameras, so I'm always getting a 100% charge.